Learning Goals

Students will:
 learn what air masses are
 explain what happens when air masses
meet
 learn how pressure systems affect the
weather
3-Minute Warm Up

1.
2.
3.
Are these statements true? If not,
correct them.
Air pressure pushes only in a
downward motion.
The Coriolis effect influences air motion
across Earth’s surface.
The changing of a gas to a liquid is
evaporation.
3-Minute Warm Up
Are these statements true? If not, correct
them.
1. Air pressure pushes only in a downward
motion. False-Air pressure pushes in all
directions
2. The Coriolis effect influences air motion
across the Earth’s surface. True
3. The changing of a gas to a liquid is
evaporation. False-The changing of a gas to a
liquid is condensation

Air masses are large bodies of air
air mass—a large body of air, in which
temperature and humidity are nearly the
same at different locations but the same
altitude.
 Covers a large area—thousands of
kilometers
 Takes on characteristics of land or water
below it
 Classified (described) by 2 characteristics:

 moisture
 temperature
Characteristics of air masses

Air masses are named
by their characteristics
 Moisture:
○ continental—dry
air, forms over land
○ maritime—moist
air, forms over
water
 Temperature:
○ Tropical—warm air
from the equator
○ Polar—cool air
Ex: continental tropical air mass—dry and warm air mass
from the poles
maritime polar—moist and cool air mass
Weather changes where air
masses meet
 Air
masses move due to global winds
and jet streams.
 When a new air mass meets and moves
into another air mass, the weather
changes
 front—a boundary between air masses
Fronts and Weather
 Different
fronts produce
different types of weather.
 3 types of fronts
 Cold front
 Warm front
 Stationary front
Cold Fronts
Cold Front

cold front—cold air mass
pushes a warm air mass
and forces warm air to
rise quickly to form tall
clouds (cumulonimbus). It
brings brief heavy storms.
Warm Fronts
Warm Front

warm front—warm air
mass moves over a
mass of denser, colder
air. It brings many hours
of steady rain or snow.
Stationary Fronts
Stationary Front

stationary front—cold
and warm air mass
pushes against each
other without moving.
Weather Systems: High and Low
Weather Systems: High and Low


high-pressure system—
formed when air sinks down
in a high pressure center
and spreads out toward low
pressure areas in a
clockwise motion.
It brings clear skies and
calm or gentle breezes.


low-pressure system—
formed when air moves
counterclockwise around
into a low pressure center,
then it moves up to higher
altitudes.
It brings stormy weather.
www.bom.gov.au/lam/Students
_Teachers/pressure.shtml